The moment came in 1974, shortly after he had inspired the Oakland Athletics to three straight World Series victories, and won what would prove his only Cy Young award. Hunter discovered that Charlie Finley, the A's owner, had violated a part of the player's then $100,000-a-year contract. Hunter took legal action, and the contract was voided. Briefly he was terrified: "I didn't have a job, I didn't realise the implications of what was happening." He soon did. Within weeks, all but one of the 24 major league teams made offers for his services. The winners were the New York Yankees, who signed Hunter to a five-year deal worth $3.35m, making him the highest-paid player in baseball by far.
What Hunter had achieved was not quite free agency: that only came in a separate case in 1975, when the US courts threw out the so-called "reserve clause" which could tie players to a single club almost for ever. But, for his colleagues in baseball, he had unlocked the future by showing them the true market value of a star performer. From then on American, and ultimately world sport, would never be the same, as power moved, slowly but unstoppably, from the clubs and governing sports federations to the players themselves.
In America, the trend spread from baseball to basketball and football; later the revolution would engulf soccer, rugby and every other professional team sport around the world. The 1996 Bosman ruling which permits European footballers total freedom at the end of their contracts is a linear descendant of Catfish Hunter's ground-breaking case.
In retrospect, the landmark 1974 decision marked the apogee of his career on the pitcher's mound. Though he notched up 23 victories in his first season in New York, and a place on the Yankees' triumphant World Series teams of 1977 and 1978, injury was taking its toll and when his contract ended he retired at the comparatively early age of 33 from the game he had graced for 15 years. In truth, leaving the Bronx was no hardship; ever the country boy, he joyously returned to his farm outside Hertford, the tiny North Carolina town where he had been born in 1946, and his favourite pastimes of fishing and hunting.
Hunter had learnt his pitching skills the old-fashioned way; taught the rudiments by his elder brothers, he perfected the accuracy that would become his trademark by ceaselessly throwing baseballs at a hole in the barn door. But his colourful nickname was something of a fraud, thrust upon him by Charlie Finley along with a legend that he had once run away from home and then placated his mother by returning with two catfish. She always hated the story, and throughout his life Hertford knew him as plain "Jimmy".
His last public appearance was in March at the Yankees' spring training in Florida, among a new generation of players who were, partly thanks to him, being paid anything up to $70m for five years' work. By then however Hunter had been diagnosed with amyotropic lateral sclerosis, or Lou Gehrig's disease, a rapidly advancing neurological illness for which no cure is known.
James Augustus ("Catfish") Hunter, baseball player: born Hertford, North Carolina 8 April 1946; married (two sons, one daughter); died Hertford 9 September 1999.